Method for preparing membrane electrode gradient catalyst layer

Abstract

The application relates to a preparation method of a membrane electrode gradient catalyst layer, belonging to the field of fuel cells. The preparation method comprises slit coating a base film by using a multi-channel die; wherein the multi-channel die is provided with a plurality of channels for outputting catalyst slurry and a lip opening in communication with the channels and used for coating the catalyst slurry on the base film, the lip opening is in a slit shape, and the catalyst slurry output by each channel is different; the slit coating comprises the following steps: when coating switching is performed on two adjacent channels, the lip opening and the base film are always filled with the catalyst slurry. The method can alleviate the problem that the fusion position of the two adjacent coating layers is uneven during the preparation of the gradient catalyst layer, thereby affecting the coating quality of the catalyst layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cells, and in particular, to a preparation method of a membrane electrode gradient catalyst layer. BACKGROUND

[0002] Proton exchange membrane fuel cells (PEMFC) have high energy density, high efficiency and environmental friendliness, and thus are attracting more and more attention in stationary and transportation applications. The membrane electrode includes a catalyst layer, a diffusion layer and a proton exchange membrane, which provides a continuous channel for protons, electrons, reaction gas and water for the electrochemical reaction of the proton exchange membrane fuel cell. Existing studies show that the performance of the PEMFC can be improved by introducing an in-plane gradient in the catalyst layer. The in-plane gradient of the catalyst layer can include various in-plane gradients such as a Pt loading gradient, an ionomer content gradient and a ratio of ionomer to carbon in the catalyst from the reaction gas inlet side to the outlet side.

[0003] In the existing preparation of the gradient catalyst layer with an in-plane gradient, a plurality of different catalyst slurries are usually used for coating, and the in-plane gradient is achieved by splicing the coating layers. However, there is a problem of uneven fusion of the adjacent two coating layers in the preparation process, that is, the thickness of the fusion of the two coating layers is inconsistent with that of the non-fusion, which affects the coating quality of the catalyst layer. SUMMARY

[0004] The present application provides a preparation method of a membrane electrode gradient catalyst layer, which can alleviate the problem of uneven fusion of the adjacent two coating layers in the preparation process of the gradient catalyst layer, which affects the coating quality of the catalyst layer.

[0005] Embodiments of the present application are implemented as follows:

[0006] The present application provides a preparation method of a membrane electrode gradient catalyst layer, which can alleviate the problem of uneven fusion of the adjacent two coating layers in the preparation process of the gradient catalyst layer, which affects the coating quality of the catalyst layer.

[0007] The multi-channel die is provided with a plurality of flow channels for outputting catalyst slurries, and a lip opening in communication with each flow channel for coating the catalyst slurry to the base film. Each lip opening is in the form of a slit, and the catalyst slurry output by each flow channel is different.

[0008] The slit coating includes that when the adjacent two flow channels are switched, the lip opening and the base film are configured to be filled with the catalyst slurry at all times.

[0009] The preparation method of the membrane electrode gradient catalyst layer provided by the application has the advantages that the distance between the base film and the lip is kept unchanged during the coating process, so that the lip and the base film are always filled with catalyst slurry when the coating switching is performed by the adjacent two flow channels, which is beneficial to keeping the fusion area of the coating formed during the switching process flat and the thickness of the large surface of the coating substantially unchanged, thereby improving the coating quality of the catalyst layer.

[0010] In some embodiments, the number of lips is multiple, and the multiple lips correspond to and communicate with the flow channels one by one.

[0011] The slot coating comprises: multiple lips are arranged at intervals along the coating direction, and any adjacent lips are sequentially switched for intermittent coating in the order from downstream to upstream along the coating direction, wherein when the coating switching is performed by the adjacent two lips, the lip located upstream along the coating direction and the base film are configured to be always filled with catalyst slurry.

[0012] In some embodiments, when the coating switching is performed by the adjacent two lips, the lip located upstream along the coating direction starts feeding after the lip located downstream along the coating direction stops feeding at the preset position of the base film.

[0013] In some embodiments, the multiple flow channels are arranged in parallel, and the spacing distance between the adjacent two lips is 3-5 mm.

[0014] In some embodiments, the number of flow channels is two.

[0015] In some embodiments, the spacing distance between the lip and the base film during the coating is 100-300 μm.

[0016] In some embodiments, the speed of the coating is 2-6 m / min, and the flow rate of the catalyst slurry is 40-120 mL / min.

[0017] In some embodiments, the lip has a width and a length perpendicular to each other, and the direction in which the lip and the coating direction are parallel is taken as the width of the lip, the width of the lip is 125-625 μm, and the length of the lip is 150-350 mm.

[0018] In some embodiments, the preparation method comprises: periodically performing slot coating on the base film along the coating direction, performing blanking treatment on the base film between the steps of the adjacent two slot coating, and the blanking length of the base film along the coating direction is ≥10 mm.

[0019] In some embodiments, the base film is a proton exchange membrane or a transfer film. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0021] Figure 1 A schematic diagram of slit coating provided for Embodiment 1 of the present application;

[0022] Figure 2 A schematic diagram of a gradient catalyst layer provided for Embodiment 1 of the present application.

[0023] Figure: 10-proton exchange membrane; 20-double channel die; 21-first channel; 22-second channel; 30-gradient catalyst layer; 31-first coating layer; 32-second coating layer; 33-fusion zone. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with reference to the embodiments, but those skilled in the art will understand that the following embodiments are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased on the market.

[0025] The unevenness of the fusion of the two adjacent coating layers includes the fusion zone protruding from the large surface of the coating layer (non-fusion zone) and the fusion zone recessed from the large surface of the coating layer, which affects the coating quality of the catalyst layer and in turn affects the performance of the battery. When the fusion zone protrudes from the large surface of the coating layer, since the fuel cell uses multiple membrane electrodes to stack, the cumulative thickness difference after superposition is too large, which easily causes the membrane electrode to be damaged when the fuel cell is stacked, affecting the gas tightness of the fuel cell. When the fusion zone is recessed from the large surface of the coating layer, the loading of the fusion zone is reduced, resulting in substandard performance of the membrane electrode.

[0026] The following will specifically describe the preparation method of the membrane electrode gradient catalyst layer according to the embodiments of the present application:

[0027] The present application provides a preparation method of a membrane electrode gradient catalyst layer, which comprises: using a multi-channel die to perform slit coating on a base film.

[0028] Among them, the multi-channel die is provided with a plurality of flow channels outputting catalyst slurry, and a lip port in communication with each flow channel for coating the catalyst slurry on the base film, the lip port is in the form of a slit, and the catalyst slurry output by each flow channel is different.

[0029] The slot coating comprises: when the two adjacent flow channels are switched for coating, the gap between the lip and the base film is configured to be filled with catalyst slurry at all times.

[0030] It can be understood that the catalyst slurry output by each flow channel is different, and the difference here can be manifested as different selection of ingredients, or different contents of the same ingredients, or different ingredients and contents, so that after the coating is formed, each catalyst coating and the fusion zone of the adjacent two coatings form an in-plane gradient.

[0031] In summary, the preparation method of the membrane electrode gradient catalyst layer provided in the application has the advantages that, since the distance between the base film and the lip remains unchanged during the coating process, when the two adjacent flow channels are switched for coating, the gap between the lip and the base film is configured to be filled with catalyst slurry at all times, which is beneficial to making the fusion zone of the coating formed during the switching process flat and substantially consistent with the thickness of the large surface of the coating, thereby improving the coating quality of the catalyst layer.

[0032] In some embodiments, the number of lips is multiple, and the multiple lips are in one-to-one correspondence with and communicate with the flow channels.

[0033] The slot coating comprises: the multiple lips are arranged at intervals along the coating direction, and any adjacent lips are switched in sequence from downstream to upstream of the coating direction for intermittent coating, wherein when the two adjacent lips are switched for coating, the lip located upstream of the coating direction and the base film are configured to be filled with catalyst slurry at all times.

[0034] That is, the multi-flow channel die is provided with multiple flow channels for outputting catalyst slurry, and each flow channel has a lip for coating the catalyst slurry on the base film.

[0035] The upstream of the coating direction refers to the side close to the coating layer that has been coated during the coating process, and the downstream of the coating direction refers to the side away from the coating layer and about to be coated during the coating process.

[0036] The intermittent coating refers to that when the previous lip stops slot coating, the next lip starts slot coating.

[0037] The intermittent coating in sequence from downstream to upstream of the coating direction for any adjacent two lips refers to that, among any adjacent two lips, the lip located downstream of the coating direction is first started for slot coating, and after the coating is completed, the lip is closed, and the lip located upstream of the coating direction is started for slot coating, so as to complete the switching of the two adjacent lips for intermittent coating. That is, the multiple lips are switched in sequence from downstream to upstream of the coating direction for intermittent coating.

[0038] Since the distance between the base film and the lip is always kept unchanged during the slot coating process, and since any two adjacent lips switch in turn from downstream to upstream in the coating direction, when the lip downstream in the coating direction finishes the slot coating and closes, and before the other lip upstream in the coating direction is opened, the space between the lip upstream in the coating direction and the base film is filled with the catalyst slurry, which can effectively avoid the problem of the fusion zone of the finally formed coating being too thin and / or too thick due to the lack of slurry or too much slurry during the switching process, affecting the coating quality of the catalyst layer, leading to defects in the performance of the membrane electrode, and affecting the performance of the subsequent fuel cell.

[0039] In addition, each lip corresponds to output different slurries, which not only has a lower difficulty in manufacturing the multi-channel die, but also can avoid the interference of different catalyst slurries with each other, affecting the performance of the gradient catalyst layer.

[0040] The switching of the two adjacent lips can be performed simultaneously or delayed.

[0041] In some embodiments, when the two adjacent lips switch, the lip downstream in the coating direction stops feeding at the preset position of the base film, and the lip upstream in the coating direction starts feeding.

[0042] In some embodiments, when the two adjacent lips switch, the lip downstream in the coating direction stops feeding at the preset position of the base film, and the lip upstream in the coating direction starts feeding.

[0043] That is, the switching of the two adjacent lips is delayed, and the delay time can be obtained by the coating speed and the interval between the two adjacent lips.

[0044] Through the above-mentioned delayed switching, it is beneficial to further alleviate the risk of the fusion zone being protruded, so that the thickness of the fusion zone of the coating layer formed during the switching process is consistent with that of the large surface of the coating layer, and the coating quality of the catalyst layer is improved.

[0045] In some embodiments, the plurality of channels are arranged in parallel, and the interval distance between the two adjacent lips is 3-5 mm.

[0046] The interval distance refers to the shortest straight line distance between the side walls of the two lips.

[0047] The interval distance is within the above range, the coating stability is good, and the thickness of the fusion zone of the coating formed during the switching process and the large surface of the coating is consistent. If the interval distance is too small, the rigidity between the two lips is insufficient, the slurry cannot be stably output, and the coating stability is poor. If the interval distance is too wide, it is difficult to realize that the lip upstream of the coating direction and the base film are configured to be filled with catalyst slurry at all times, and the fusion zone of the two coatings is uneven, which affects the coating quality of the catalyst layer.

[0048] In some embodiments, the number of flow channels is two.

[0049] The two flow channels meet the requirements of the preparation of the membrane electrode gradient catalyst layer for fuel cells, and the double-flow channel die is easy to prepare.

[0050] In some embodiments, the interval distance between the lip and the base film during coating is 100-300 μm.

[0051] Within the above range, the gradient catalyst layer formed meets the use requirements of the membrane electrode.

[0052] Exemplarily, the interval distance between the lip and the base film during coating is any value or between any two values in 100 μm, 150 μm, 200 μm, 250 μm, and 300 μm.

[0053] In some embodiments, the coating speed is 2-6 m / min, and the flow rate of the catalyst slurry is 40-120 mL / min.

[0054] The flow rate and the coating speed cooperate to obtain a coating with good thickness uniformity.

[0055] Exemplarily, the coating speed is any value or between any two values in 2 m / min, 3 m / min, 4 m / min, 5 m / min, and 6 m / min.

[0056] Exemplarily, the flow rate of the catalyst slurry is any value or between any two values in 40 mL / min, 60 mL / min, 80 mL / min, 100 mL / min, and 120 mL / min.

[0057] In some embodiments, the lip has a width and a length perpendicular to each other, and the direction parallel to the coating direction when slit coating is performed is taken as the width of the lip. The width of the lip is 125-625 μm, and the length of the lip is 150-350 mm.

[0058] Within the above range, the slit coating effect is good.

[0059] In some embodiments, the preparation method comprises: periodically performing slot coating on the base film in a coating direction, performing blanking treatment on the base film between two adjacent slot coating steps, and the blanking length of the base film in the coating direction is ≥10 mm.

[0060] The blanking treatment refers to not performing slot coating on the base film, so that the surface of the base film is free of any catalyst coating, thereby realizing continuous preparation of the gradient catalyst layer with a spacing distribution, so as to facilitate subsequent cutting at the blanking position to obtain a target membrane electrode and improve the preparation efficiency.

[0061] Optionally, the catalyst loading in the gradient catalyst layer of the membrane electrode is 0.05-0.5 mg / cm 2 .

[0062] Illustratively, the catalyst loading in the gradient catalyst layer of the membrane electrode is any one of 0.05, 0.1 mg / cm 2 , 0.2 mg / cm 2 , 0.3 mg / cm 2 , 0.4 mg / cm 2 , 0.5 mg / cm 2 or between any two values.

[0063] Optionally, the width of the fusion zone in the coating direction formed by the catalyst slurry coated by the two adjacent flow channels in the gradient catalyst layer of the membrane electrode is 5-10 mm.

[0064] The width of the fusion zone of the gradient catalyst layer of the membrane electrode prepared by the above method is relatively narrow, which effectively improves the coating quality of the catalyst layer.

[0065] Optionally, during the slot coating process, the coating layer formed is also subjected to blanking treatment in the width direction thereof and the base film, thereby facilitating subsequent cutting. The width of the coating layer is the straight-line distance between the two edges of the coating layer on both sides in the coating direction.

[0066] In some embodiments, the base film is a proton exchange membrane or a transfer film. The preparation method of the gradient catalyst layer of the membrane electrode of the present application is described in further detail below in combination with embodiments.

[0067] Embodiment 1

[0068] This embodiment prepares a gradient catalyst layer, which mainly comprises the following steps:

[0069]

Preparation of the first catalyst slurry

[0070] 5 g of platinum / carbon catalyst and 14 g of perfluorosulfonic acid resin solution (perfluorosulfonic acid resin content is 15%) are dispersed in 70 g of mixed solvent to prepare, and the mixed solvent is an aqueous solution of ethanol, and the mass fraction of ethanol is 40%.

[0071] Preparation of the second catalyst slurry

[0072] The catalyst was prepared by dispersing 6g of platinum / carbon catalyst and 14g of perfluorosulfonic acid resin solution (perfluorosulfonic acid resin content was 15%) in 70g of mixed solvent, the mixed solvent being an aqueous solution of ethanol with a mass fraction of 40%.

[0073] Slot coating

[0074] like Figure 1 As shown, the arrow indicates the coating direction (the proton exchange membrane 10 moves in the opposite direction of the coating direction during coating). Coating is performed using a dual-channel die 20. The dual-channel die 20 has a first channel 21 and a second channel 22 that are parallel to each other, as well as a first lip and a second lip that are parallel to each other. The first channel 21 is connected to the first lip, and the second channel 22 is connected to the second lip. The distance G between the first lip and the second lip is 4 mm. The width of the first lip and the second lip is 400 μm, and the length of the lip is 200 mm.

[0075] The first flow channel 21 is used to output the first catalyst slurry, and the second flow channel 22 is used to output the second catalyst slurry. The flow rates of both the first catalyst slurry and the second catalyst slurry are 100 mL / min.

[0076] The distance between each lip and the proton exchange membrane 10 is 200 μm. The first lip and the second lip are arranged alternately along the coating direction, with the first lip located downstream of the second lip in the coating direction.

[0077] When preparing the gradient catalyst layer 30, a first coating layer 31 with a length of 200 mm in the coating direction is first applied using a first lip. Simultaneously, the supply of the second catalyst slurry is started while the first lip stops coating, causing the second lip to begin feeding and coating a second coating layer 32 with a length of 200 mm. During the switching between the first and second lip coating processes, the space between the second lip and the base film is always filled with catalyst slurry. The coating speed is 4 m / min. The coated catalyst layer is then dried and rolled up.

[0078] The catalyst layer obtained during preparation is as follows Figure 2 As shown.

[0079] Example 2

[0080] The difference between it and Example 1 is that:

[0081] In the [slit coating] step, the distance G between the first lip and the second lip is 5 mm. Example 3

[0082] The difference between it and Example 1 is that:

[0083] In the step of slit coating, the distance G between the first lip and the second lip is 3 mm.

[0084] Comparative Example 1

[0085] The difference between it and Example 1 is only that:

[0086] The first flow channel 21 is used to output the second catalyst slurry, and the second flow channel 22 is used to output the first catalyst slurry.

[0087] When the gradient catalyst layer 30 is prepared, the first coating layer 31 with a length of 200 mm in the coating direction is coated by using the second lip first, the supply of the first catalyst slurry is stopped by the valve control while the supply of the second catalyst slurry is started, the second lip stops coating while the first lip starts feeding and coating the second coating layer 32 with a length of 200 mm, and there is a situation that the first lip is not filled with catalyst slurry between the first lip and the base film when the first lip and the second lip switch the coating.

[0088] Test Example 1

[0089] The thicknesses of the first coating layer 31, the second coating layer 32, and the fusion zone 33 of the first coating layer 31 and the second coating layer 32 in Example 1-3 and Comparative Example 1 are measured by using a thickness gauge. The results are shown in Table 1.

[0090] Among them, the average thickness is the average value calculated by randomly selecting the thicknesses of 15 random points in the first coating layer 31, the second coating layer 32, or the fusion zone 33 as the average thickness of the corresponding first coating layer 31, second coating layer 32, or fusion zone 33.

[0091] Table 1 Thicknesses of the catalyst layers of Example 1-3 and Comparative Example 1

[0092]

[0093] According to Table 1, the average thickness of the fusion zone in Example 1-3 of the application is small, and the coating quality of the catalyst layer is good. In Comparative Example 1, the coating sequence of the first lip and the second lip is changed during the coating process, which causes the first lip to be not filled with catalyst slurry between the first lip and the base film when the coating is switched, which causes the average thickness of the fusion zone to be significantly lower than the average thicknesses of the first coating layer and the second coating layer, and the coating quality of the catalyst layer is poor.

[0094] The above is only a specific embodiment of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a gradient catalyst layer for a membrane electrode, characterized in that, The preparation method includes the following steps: using a multi-channel die head to perform slit coating on the base film; The multi-channel die head has multiple channels for outputting catalyst slurry and a lip that communicates with each channel for coating the catalyst slurry onto the base film. The lip is slit-shaped. The catalyst slurry output by each channel is different. There are multiple lips. The multiple lips correspond one-to-one with the channels and are connected. The multiple channels are arranged in parallel. The interval between two adjacent lips is 3-5 mm. The slit coating includes: a plurality of lips arranged at intervals along the coating direction, and any adjacent lips sequentially switching to perform intermittent coating in the order from downstream to upstream of the coating direction, wherein the base film moves in the opposite direction of the coating direction during coating, and when two adjacent lips switch coating, the lip located upstream of the coating direction and the base film are configured to always be filled with the catalyst slurry.

2. The preparation method according to claim 1, characterized in that, When two adjacent lips switch coating, after the lip located downstream in the coating direction stops feeding at a preset position of the base film, the lip located upstream in the coating direction starts feeding.

3. The preparation method according to any one of claims 1-2, characterized in that, The number of flow channels is two.

4. The preparation method according to any one of claims 1-2, characterized in that, The distance between the lip and the base film during coating is 100-300 μm.

5. The preparation method according to any one of claims 1-2, characterized in that, The coating speed is 2-6 m / min, and the flow rate of the catalyst slurry is 40-120 mL / min.

6. The preparation method according to any one of claims 1-2, characterized in that, The lip has a width and length that are perpendicular to each other. The width of the lip is defined as the direction in which the lip is parallel to the coating direction when performing slit coating. The width of the lip is 125-625μm, and the length of the lip is 150-350mm.

7. The preparation method according to any one of claims 1-2, characterized in that, The preparation method includes: periodically performing slit coating on the base film along the coating direction, leaving a blank between two adjacent slit coating steps, wherein the blank length of the base film in the coating direction is ≥10mm.

8. The preparation method according to any one of claims 1-2, characterized in that, The base membrane is a proton exchange membrane or a transfer membrane.

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